1. Field of the Invention
The present application relates to charge pumps and more particularly to charge pumps suitable for use in integrated circuits.
2. Background of the Technology
A charge pump is a circuit topology that is designed to produce a voltage at a higher potential than that provided by a source. Charge pumps may be used in a wide variety of applications, including, but not limited to, serving as power supplies for passive RFID (radio frequency identification) circuits.
If the source/input to the charge pump is of single polarity, a charge pump generically must be of the form disclosed by IEEE Journal of Solid-State Circuits, vol. SC-11, No. 3, (June 1976), using different clock phases. Most MOS charge pumps are of this form, as reflected by U.S. Pat. Nos. 6,137,344, 6,198,342, and 6,501,325. This form of charge pump relies on alternate phases of a clock to spill the charges through the MOS device while it is in a conduction mode, and block the reverse flow of charge back through the device by a clock phase that turns the device off during the back cycle. This form of charge pump is an active-mode charge pump, requiring external clocks and power rails.
If the source is of alternating polarity voltage, whether sinusoidal power source or radio-frequency signal, then the charge pump is of the form of an AC-DC converter, and the sequence of charge pump stages provides a single polarity output with voltage multiplication. The source must be of alternating polarity for the charge to be lifted to higher voltage levels at the output, with the MOS device as a diode construct. This form of charge pump is a passive-mode charge pump, requiring no external clock phases or power rails. The passive mode type of charge pump is fairly rare. The only known examples are U.S. Pat. Nos. 6,549,064 and 6,819,162. The charge pumps disclosed by these two patents use a mix of capacitors and MOSFETs. For U.S. Pat. No. 6,549,064 each stage consists of 3 MOSFETs and 2 capacitors, with two of the MOSFETs configured to act as diodes and the remaining transistor configured as a regular MOSFET device. U.S. Pat. No. 6,819,162 a negative voltage is induced by a plurality of pump stages, with each stage consisting of 4 MOSFETS, 4 diodes, and 2 capacitors.
All charge pumps require a diode-capacitance action in order to accomplish the capture and accumulation of charge, relying on either clock phasing or alternating polarity to invoke the on-off diode action necessary for functionality. Even though the MOSFET is a capacitance construct is unusual to use the MOSFET as a capacitor. The only known instance in which MOSFETs are used in this manner is U.S. Pat. No. 6,166,585. For this patent, the MOS capacitances are devised as simple capacitors, driven by phased clocks and supplied by power rails as an active mode form of charge pump.
The charge pumps disclosed in the aforementioned prior art suffer from various drawbacks, including either a need for external clock circuitry or overly complex designs using a mix of capacitors, diodes and MOSFETs.